Image copyright Getty Images Image caption Measures taken in 449 US children revealed traces of lead in more than half
More than half of children in the US had traces of lead in their blood in 2016, a study has found.
Babies born to mothers with blood lead levels over 10 micrograms per decilitre (ng/dL) were four times more likely to develop attention problems.
In seven-year-olds, more than a quarter had detectable levels of lead.
Lead exposure can damage parts of the brain and nervous system, affecting learning, attention and behaviour.
Lead exposure in children is thought to contribute to ADHD – attention deficit hyperactivity disorder.
New research published in Environmental Health Perspectives, a journal of the US National Institutes of Health, found that levels of lead in blood were higher among black children than white children.
Image copyright Getty Images Image caption Children are considered at risk if their blood lead levels exceed 15 ng/dL
Lead was detected in 55.2% of black children in 2016, compared with 20.3% of white children.
Lead levels were higher among children at the highest risk – those whose mothers had blood lead levels above 10 ng/dL – than the lowest risk group.
The study’s findings were based on the blood lead levels measured on 2,522 samples taken from parents and adolescents in 2016, among children aged 5-14, during visits to 12 US clinical practices.
The subjects were evaluated using the US Joint Commission Centre for Professional Quality Framework, designed to assess and track child development.
Because of health programmes and childhood lead poisoning prevention, which in some cases have reduced birth-weight and extreme cases of lead poisoning, total blood lead levels decreased over the past two decades.
That is consistent with US Centers for Disease Control and Prevention data.
However, there is ongoing uncertainty about how lead exposure in adults has affected children in the US, the study’s authors say.
The authors recommended that blood lead levels in children be calculated using new regulatory standards to update the current system, which was developed in 2004, which required that lead levels be at or below 0.05 ng/dL.
Why blood lead levels increase with age
A century ago, the US suffered from a crisis of lead poisoning in children.
In some cases, babies were severely poisoned and died of illness or premature death. The common uses of lead for household products or in industry led to steady increases in lead exposure from the late 19th Century through the 1950s and to the 1970s.
In the 1980s, several state governments adopted legislation designed to reduce or eliminate the use of lead. But as lead levels declined in blood samples, public health campaigns to decrease exposure deteriorated.
Today, public health campaigns to reduce levels of lead are focused on children, who have continued to experience higher levels of lead exposure than adults, especially in younger children.
The Institute of Medicine (IOM) reported on the science of lead exposure in children in 2007, based on a review of research on exposure from 18 countries.
Published two years later, the report concluded: “The risks associated with lead are very real and may exist in infants, toddlers, preschoolers, preschoolers, and children between the ages of 4 and 15 years.
“This is a burden that must be faced openly and honestly by each person with a child.”
Lead in the blood has been the subject of scientific study and has been reduced – though an increase in preschoolers over the past 15 years has raised new concerns.
Lead in high concentrations is harmful to body function. An excess of lead exposure may increase an individual’s risk of blood vessel damage and damage the kidneys, which may lead to a worse kidney function.
And whether or not lead exposure leads to any adverse effects depends on the individual and a range of other factors.
Determining how to reduce a lead level in blood is like a litmus test of the developmental, cognitive and behavioural skills of a child.
A healthy lead level is below 15 ng/dL.
It is likely the average blood lead level is much higher for black children, because many living in inner-city communities have their bodies exposed to lead in the form of paint and dust.
However, the study’s authors said that although a far higher proportion of black children were at increased risk of elevated blood lead levels, the overall average blood lead level in children is higher in all races.
The study had “strange results”, said Dana Alatzas, professor of the environmental health division at the University of Florida, who was not involved in the study.
“These data suggest